package-infra: limit the number of // jobs

From: "Yann E. MORIN" <yann.morin.1998@free.fr>

The current code spawns as many jobs as up to twice the number of CPUs.

On small-class machines like laptops, with a limitted amount of memory,
but still a few CPUs (real or hyperthreads), the HDD becomes a bottleneck,
and it becomes almost impossible to do anythiong else while there is a
build in progress.

Limit the number of jobs to the number of CPUs plus one.

Even on fast machines with fast HDDs, this settings keeps the machine
fully busy (for those packages that can build in parallel, of course).

For example, building qemu or the linux kernel kept my hyperthreaded
hexa Core i7 with 18GiB of RAM, busy at 99% (I never ever managed to
get 100% even with more jobs, not even 200); while on my hyperthreaded
dual Core i5 with only 4GiB and a slow HDD, I still topped at 100% CPU,
while still able to do some work involving the HDD.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
---
 package/Makefile.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

All,

On Fri, May 10, 2013 at 12:03:20AM +0200, Yann E. MORIN wrote:
[--SNIP--]
> Limit the number of jobs to the number of CPUs plus one.
[--SNIP--]
> @@ -11,7 +11,7 @@ HOSTMAKE :=$(shell which $(HOSTMAKE) || type -p $(HOSTMAKE) || echo make)
>  # while waiting on I/O.
>  ifeq ($(BR2_JLEVEL),0)
>  PARALLEL_JOBS:=$(shell echo \
> -	$$((2 * `getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1`)))
> +	$$((2 + `getconf _NPROCESSORS_ONLN 2>/dev/null || echo 0`)))

I forgot to 'git add' before I 'git commit --amend'.
So this should have been a '1 +' not a '2 +'.

Sigh... :-/

Regards,
Yann E. MORIN.

Hi Yann,

On Fri, 2013-05-10 at 00:03 +0200, Yann E. MORIN wrote:
> From: "Yann E. MORIN" <yann.morin.1998@free.fr>
> 
> The current code spawns as many jobs as up to twice the number of CPUs.
> 
> On small-class machines like laptops, with a limitted amount of memory,
> but still a few CPUs (real or hyperthreads), the HDD becomes a bottleneck,
> and it becomes almost impossible to do anythiong else while there is a
> build in progress.
> 
> Limit the number of jobs to the number of CPUs plus one.
> 
> Even on fast machines with fast HDDs, this settings keeps the machine
> fully busy (for those packages that can build in parallel, of course).
> 
> For example, building qemu or the linux kernel kept my hyperthreaded
> hexa Core i7 with 18GiB of RAM, busy at 99% (I never ever managed to
> get 100% even with more jobs, not even 200); while on my hyperthreaded
> dual Core i5 with only 4GiB and a slow HDD, I still topped at 100% CPU,
> while still able to do some work involving the HDD.
> 
> Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
> ---
>  package/Makefile.in | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/package/Makefile.in b/package/Makefile.in
> index a449089..a575f17 100644
> --- a/package/Makefile.in
> +++ b/package/Makefile.in
> @@ -11,7 +11,7 @@ HOSTMAKE :=$(shell which $(HOSTMAKE) || type -p $(HOSTMAKE) || echo make)
>  # while waiting on I/O.
>  ifeq ($(BR2_JLEVEL),0)
>  PARALLEL_JOBS:=$(shell echo \
> -	$$((2 * `getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1`)))
> +	$$((2 + `getconf _NPROCESSORS_ONLN 2>/dev/null || echo 0`)))

You'll need to update/remove the comment preceding this code too...

When I submitted this feature there was some discussion of what the
heuristic should be here.  Given your experience I am fine with making
it more conservative, especially since this is the default behavior.

Nathan, All,

On Fri, May 10, 2013 at 08:09:11AM -0500, Nathan Lynch wrote:
> On Fri, 2013-05-10 at 00:03 +0200, Yann E. MORIN wrote:
> > From: "Yann E. MORIN" <yann.morin.1998@free.fr>
> > 
> > The current code spawns as many jobs as up to twice the number of CPUs.
> > 
> > On small-class machines like laptops, with a limitted amount of memory,
> > but still a few CPUs (real or hyperthreads), the HDD becomes a bottleneck,
> > and it becomes almost impossible to do anythiong else while there is a
> > build in progress.
> > 
> > Limit the number of jobs to the number of CPUs plus one.
> > 
> > Even on fast machines with fast HDDs, this settings keeps the machine
> > fully busy (for those packages that can build in parallel, of course).
> > 
> > For example, building qemu or the linux kernel kept my hyperthreaded
> > hexa Core i7 with 18GiB of RAM, busy at 99% (I never ever managed to
> > get 100% even with more jobs, not even 200); while on my hyperthreaded
> > dual Core i5 with only 4GiB and a slow HDD, I still topped at 100% CPU,
> > while still able to do some work involving the HDD.
> > 
> > Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
> > ---
> >  package/Makefile.in | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/package/Makefile.in b/package/Makefile.in
> > index a449089..a575f17 100644
> > --- a/package/Makefile.in
> > +++ b/package/Makefile.in
> > @@ -11,7 +11,7 @@ HOSTMAKE :=$(shell which $(HOSTMAKE) || type -p $(HOSTMAKE) || echo make)
> >  # while waiting on I/O.
> >  ifeq ($(BR2_JLEVEL),0)
> >  PARALLEL_JOBS:=$(shell echo \
> > -	$$((2 * `getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1`)))
> > +	$$((2 + `getconf _NPROCESSORS_ONLN 2>/dev/null || echo 0`)))
> 
> You'll need to update/remove the comment preceding this code too...

Right, good catch. I'll send an updated patch soonish.

> When I submitted this feature there was some discussion of what the
> heuristic should be here.  Given your experience I am fine with making
> it more conservative, especially since this is the default behavior.

Yes. In the Good Old Times (TM), it was customary to set jobs=2*CPU,
because disks (or network) was very slow, and IO did not catch up with
CPU bandwidth; this is not much true these days.

Regards,
Yann E. MORIN.